Ophthalmologists and optometrists would like to have an accurate representation of subjects' eyes. Such representations include, for example, one or more of a representation of a subject's corneal anterior surface, posterior surface, and corneal thickness and density, as well as anterior chamber profiles. This information may be used to prescribe contact lenses and eye glasses, and to reshape the cornea by surgical procedures or to perform other surgical procedures. Since it is not comfortable to measure these data with physical contact, remote sensing techniques are preferably used to perform the measurements.
One common technique for obtaining eye measurement information includes projecting narrow bands of light (commonly referred to as slits or slit beams) onto a patient's eye at multiple locations across the cornea using a slit projector and for each slit imaging a cross section of the eye. A slit projector typically includes an aperture of appropriate shape and size, and a lens placed in the path of light from a light source such that the light passing through the aperture forms a long narrow pattern of light on the subject's cornea.
Typically, to project slits at each of multiple locations across the cornea, a portion of the slit projector is moved such that the light passing through the aperture at selected times forms the multiple slits. One example of such an eye measurement apparatus, in which a portion of the slit projector is translated, is presented in U.S. Pat. No. 5,512,966 to Snook. In another embodiment, a portion of the slit projector may be rotated as described in U.S. Pat. No. 6,286,958 by Koest. In another embodiment, multiple projectors may be arranged to project slits at multiple locations on the cornea as in United States Patent Appl. No. 2007/0188709 by Van Saarloos.
In the embodiments described above, for each of the slits, after the light in the slit has been scattered by the eye, an image of a cross section of the eye is obtained. A problem with such apparatus is that, in addition to the scattered light from the slits of light, the cross sectional images typically include ambient light from sources other that the slit projectors (e.g. room lights)).